The present invention relates to input devices, in particular pointing devices such as mice, and more particularly to sleep modes for such devices.
In many instances, it is desired to bring a pointing device into a power saving mode. For example, Universal Serial Bus (USB) specifications require a low power device in suspend mode to consume less than 500 uA overall. Similarly, a wireless, battery operated pointing device must limit its power consumption to a minimum when the user is either not present or not using the device. Two strategies have been applied to reach this goal, namely the interrupt approach and the activity monitoring approach.
The interrupt approach relies on the interrupt input found in the device microcontroller. This input, when asserted, activates built-in wake-up circuitry that brings the device back into an active mode, from an idle state in which power consumption is minimal. When the device is idle, the wake-up circuitry is active but requires a very small amount of power. In this configuration, the interrupt input is connected to a switch that the user must depress to activate (wake up) the device. In the activity monitoring approach, some monitoring activity is started in a periodic manner to verify that a user is not soliciting the device in any way. In a mouse, activity monitoring requires flashing the encoder Light Emitting Diodes (LEDs) and reading back the photodetector signals in order to detect a potential horizontal movement, a rather power hungry task. If activity is detected, the device resumes an active state. In this approach, battery saving is obtained thanks to the long idle time between two activity monitoring periods. This approach is less effective than the former since monitoring typically requires more power than that required in the microcontroller idle state.
While the two approaches have proven to be very effective, both suffer from their own limitations. The interrupt approach limitation is the fact that a pointing device must be “wakened up” by clicking on a switch when in power saving mode, e.g. there is no automatic waking up when the user moves the pointing device as is currently the case in Logitech products. On the other hand, the monitoring approach doesn't require a clicking wake up action, but suffers from a rather long latency time when the device is in this monitoring mode, the shortening the latency time being in contradiction with the power saving objectives.
The problem of power consumption is particularly troublesome in the new mice using an optical module, which detects the reflection of light off a surface to determine mouse movement. When such a device is made wireless, requiring a transmitter (e.g., radio or infrared) as well, it is difficult to have the batteries last more than a couple of months. Accordingly, it is desirable to have an improved, automatic power saving mode.
As discussed below, the present invention provides such an improved power saving mode by using hand detection to activate an input device, such as a mouse. In one embodiment, the hand detection uses capacitive detection. Hand detection and capacitive detection have been used in other applications, a few of which are discussed below. For example, touchpads use capacitive detection to detect the location of a finger on a touchpad.
U.S. Pat. No. 5,341,036 is an example of hand detection being used to activate a system. In that patent, a machine operator control station is activated when both hands of the operator are detected on the control inputs.
U.S. Pat. No. 4,919,429 shows the detection of a hand by an optical beam being broken. The detection of the hand activates certain routines of a hand skill amusement game.
Capacitive switches have also been used in other applications, such as detecting the touch of a user on a lamp, and turning on the lamp.